Recently, with the rapid progress in recording technologies, it has been possible to obtain high-definition image quality substantially equal to that of silver halide photography. Accordingly, ink-jet recording apparatuses that form images by an ink-jet recording system have been widely used as image forming apparatuses.
For such ink-jet recording apparatuses, realization of high-speed image formation has been strongly desired. However, in the case where image formation is performed in an ink-jet recording apparatus at a high speed, before an ink permeates into a recording medium such as a paper, the recording medium passes through a pair of discharge rollers and is discharged, and consequently, the ink may adhere to the discharge roller (offset). In this case, an image defect tends to be generated in a formed image. In order to suppress generation of an image defect in a formed image due to offset, it is conceivable that the amount of ink to be ejected is reduced. In this case, it is difficult to form an image having a desired image density.
In view of the above circumstances, for example, an ink for an ink jet recording apparatus, the ink containing 2-n-butyl-2-ethyl-1,3-propanediol and a pigment dispersion prepared by using a resin having a weight-average molecular weight of 3,000 or more and 50,000 or less, has been proposed as an ink in which problems regarding the generation of an image defect in a formed image due to offset and the image density of a formed image are solved.
However, a further increase in the speed of image formation has been desired for ink-jet recording apparatuses. In this case, with the above-proposed ink for an ink-jet recording apparatus, above-mentioned problems regarding the generation of an image defect in a formed image due to offset and the image density of a formed image is not necessarily solved.
In the case where an ink-jet recording apparatus using a line-head recording system (hereinafter also referred to as a “line-head-type ink-jet recording apparatus”) is used, with the ink-jet recording apparatus being capable of forming an image at a high speed, unlike a serial-type ink jet recording apparatus, overwriting of an image cannot be performed. Therefore, in order to form an image having a desired image density, it is necessary to increase the amount of ink ejected, as compared with the case where a serial-type ink-jet recording apparatus is used. Accordingly, in the case where such a line-head-type ink-jet recording apparatus is used, an image defect in a formed image due to offset tends to be particularly generated. Thus, in a line-head-type ink-jet recording apparatus, it is very difficult to achieve both the suppression of generation of an image defect in a formed image due to offset and the formation of an image having a desired image density by using the above-proposed ink for an ink-jet recording apparatus.